TOXIC COMPOUNDS ISOLATED FROM MICROCYSTIS PCC7806 THAT ARE MORE ACTIVE AGAINST DAPHNIA THAN 2 MICROCYSTINS

Microcystis strain PCC7806 was toxic to Daphnia pulicaria. The toxicity of a crude water extract from lyophilized cells of Microcystis was determined in order to characterize the toxic compound. The LC50 of the crude extract was 47.4 mul ml-1. The crude extract was fractionated by solid-phase extraction and tested for toxicity. The microcystins in the different fractions were analyzed by HPLC. The crude extract contained 22 mug ml-1 microcystin-LR and 12.3 mug ml-1 3-des-methylmicrocystin-LR, the C-18 eluate contained 16.3 and 9.1 mug ml-1 of these compounds, respectively. Neither compound was detected in the C-18 cartridge-passed crude extract. Nevertheless the C-18 cartridge-passed fraction was toxic to Daphnia. Hence I conclude that the two microcystins in the crude water extract are not the compounds in Microcystis PCC7806 which are toxic to Daphnia.